This invention relates to coating compositions and molding compositions containing an amount of alkyl vinyl ether polymer effective to improve leveling and/or prevent or eliminate foam, and to the use of these copolymers for improving leveling and/or preventing or eliminating foam in coating compositions and molding compositions.
Coating compositions and molding compositions are resin systems which contain resins (natural resins and/or synthetic resins) as binders and are described below and in the referenced prior art.
It is known to use polysiloxanes or polysiloxane copolymers as leveling agents in organic resin systems for coatings. The addition of low molecular weight dimethylpolysiloxanes and methylphenylpolysiloxanes is described in German Patent Nos. DE 1,111,320 and DE 1,092,585. It is also known to use polyoxyalkylene-modified dimethylpolysiloxanes in order to achieve similar effects. ("Goldschmidt informiert" 7/1982, No. 56, page 2; 6th Fatipec Congress, 1962, page 332). It is also known to use polyacrylates of certain molecular weight ranges as leveling agents.
The disadvantage with polysiloxanes is that, insofar as they are soluble in the resin systems, they have the property of greatly reducing the surface tension. The tendency of the resin system to foam is consequently increased. Furthermore, polysiloxanes tend to cause defects in the inter-layer adhesion. It is known that products of this type are also used as release agents.
Polyacrylates, like the incompatible polysiloxanes, tend to cause cloudiness in unpigmented resin systems. The products generally used as leveling agents essentially function as a consequence of their ability to greatly reduce the surface tension, and have the disadvantages associated with reduced surface tension.
Commonly used antifoam agents likewise include polysiloxanes, polysiloxane copolymers or polyacrylates. These polymers function by virtue of their limited solubility and reduction of the surface tension. These products have a tendency, due to their pronounced incompatibility, to cause craters and cloudiness in the coating systems. If these systems are not, as is usually the case, dissolved in organic solvents, but in water or in mixtures of water and water-miscible solvents, such as butyl glycol, the crater formation is still more pronounced due to the even greater incompatibility and the greater difference in surface tension.
U.S. Pat. No. 3,127,352 describes high molecular weight polyalkyl vinyl ethers as antifoam agents for liquid hydrocarbons. These products are completely unsuitable in aqueous systems due to their incompatibility.
When used in organic systems, high molecular weight polyvinyl alkyl ethers often cause coating defects, for example in the form of leveling defects and craters. A further disadvantage of these products, accounted for by their incompatibility, is the rapid separation of the resin systems during storage. In unpigmented resin systems this incompatibility also causes pronounced cloudiness in the coating.
Polyalkyl vinyl ethers have been recommended as antifoam agents in aqueous media (U.S. Pat. No. 4,692,267). The fundamental disadvantage of these products is that they are generally incompatible in aqueous systems. According to the aforementioned patent, a slight improvement in the incorporation into aqueous media can be achieved by using emulsifiers. Such emulsifiers have, however, only a temporary effect during incorporation of the antifoam agents into the resin system. During storage of the resin systems, the incompatible substances tend to separate out from the resin system and, in the form of incompatible droplets or particles, cause defects in the coating systems.
The copolymerization of these prior art polyalkyl vinyl ethers with other monomers, such as acrylic esters or methacrylic esters is limited, since according to the literature only alternating copolymerization produces yields which are of interest industrially. If however such large amounts of (meth)acryloyl monomers are used, the essential effect of the alkyl vinyl ethers is lost.